In disc drive data storage devices, data is stored in tracks on a disc. In many systems, the data is stored in blocks on the track to allow for localized error detection and correction during reading. Typically, the blocks of data are grouped into sectors that are marked by a reference mark and/or a servo-positioning field. In many systems, the individual blocks within a sector do not include an address field and thus cannot be distinguished from other blocks except by their distance from the reference mark. To access a block, such systems initiate a timer when the reference mark is detected. When the timer expires, the read or write head is assumed to be over the desired block.
One problem with this indirect addressing scheme is that variations in the rotational speed of the disc and variations in the processing time required to identify the reference mark can cause inadequate correlation between the timer and the actual position of the head. Thus, the timer may expire before the head reaches the block or may expire after the head has already passed the beginning of the block.
To avoid having one data section written onto another data section, empty buffer fields known as spin pads are inserted between the data sections. In the past, the spin pads were a fixed size, such that each spin pad along a track had the same length. However, these fixed-length spin pads take up space that could otherwise be used to store data and as such, are an obstacle to increasing data capacity in a disc drive.
The present invention provides a solution to this and other problems, and offers other advantages over the prior art.